BIOL 311 Lecture Notes - Lecture 7: Lactose Intolerance, Lactase, Start Codon

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Published on 11 Dec 2017
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Example of En h a n c e rs Lac to s e intolerance a n d gene
expres s io n
- The enzyme lacta s e is re quired to break la ctos e into glucos e a nd galactose in human
digestion
- La cta s e e xpre ssion is significa ntly down-re gula ted (due to e nha nce d transcription) in e a rly
childhood, leading to la ctos e intole ra nce
- Without the expre s s ion of la cta s e , la ctose pas s e s to the colon, whe re it is fe rmente d by
ba cte ria producing the s ymptoms a s socia te d with la ctos e intolerance
EMERGENCE OF LACTASE P ERS IS TENCE
- La ctose pers is te nce is the condition tha t a llows a dults to dige s t la ctose. It is inhe rited in an
autos omal dominant fa shion
- How did it e me rge ?
- A cytos ine to thymine transition polymorphis m (S NP) a fe w ba ses after the 5’ of the
initia tion codon of the la ctase gene ha s be e n loca te d a nd implica te d in the obs e rva tion of
la cta s e persiste nce
- Re search ha s s hown that this S NP like ly a ppeare d ~7500 years ago in a re gion betwee n
ce ntra l Balkans a nd centra l Europe. It unde rwent positive selection a mong da iry fa rme rs
PREVENTING ENHANCERS FROM IMPROP ERLY ACTIVATING GENE EXPRES SION
- Enha ncer-blocking ins ula tor: re cruits prote ins (tha t either e na ble or preve nt e nha nceos omes
to form) that a llow DNA to get loope d
- Enha ncer must be in the s a me loop a s the promote r for e nha nce osome forma tion
- Ke y P oints
- Ge ne regula tion in e uka ryote s is s imilar to the process in proka ryote s
- However, ma ny more DNA re gulatory s eque nces a nd re gulatory prote ins a re re quired for
the process . S ome DNA regula tory seque nce s ca n be e xtremely fa r upstream from the
promote r
- Re gulatory prote ins bind to DNA regula tory e le ments , but a ls o bind to othe r re gula tory
prote ins. This a llows for the tra ns criptional ma chine ry to be recruited, a nd for chromatin
re modelling to occur
- Enha ncer-blocking ins ula tors pre vent improper enhancer a ctivation, a nd imprope r ge ne
expre s s ion
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